Lithography involves a process in which, for example, a resist film is formed from a resist material on, a substrate; the resist film is selectively exposed to a radiation such as light or an electron beam via a mask having a specific pattern; and the exposed resist film is developed, to thereby form a specific resist pattern on the film. As used herein, the term “positive tone resist material” refers to a resist material which, when exposed to light, dissolves in a developer, and the term “negative tone resist material” refers to a resist material which, when exposed to light, does not dissolve in a developer.
In recent years, with the progress of lithography techniques, micro-patterning has been rapidly developed in production of semiconductor devices or liquid crystal display devices. Generally, miniaturization of patterning is carried out by use of an exposure light source of short wavelength (higher energy). Hitherto, ultraviolet rays such as g-ray and i-ray have been used for lithography. Recently, KrF excimer laser or ArF excimer laser has been used for mass production of semiconductor devices. Also, attempts have been made to use, in lithography, F2 excimer laser, electron beams, EUVs (extreme ultraviolet rays), X-rays, etc. having a shorter wavelength (higher energy) as compared with KrF excimer laser or ArF excimer laser.
A resist material is required to exhibit various lithographic properties, including sensitivity to such an exposure light source, and resolution which realizes reproduction of micro-patterning. A resist material satisfying these requirements is, for example, a chemically amplified resist composition containing a base component whose solubility in an alkaline developer changes through the action of an acid, and an acid generator component which generates an acid through light exposure.
For example, a generally used chemically amplified positive tone resist composition contains a resin component (base resin) whose solubility in an alkaline developer increases through the action of an acid, and an acid generator component. In the case where a resist film is formed from such a resist composition, when the resist film is subjected to selective light exposure during formation of a resist pattern, an acid is generated from the photoacid generator component at an exposed portion of the film, and the solubility of the resin component in an alkaline developer increases through the action of the acid, whereby the exposed portion becomes soluble in the alkaline developer.
A photoresist composition which is currently used for, for example, ArF excimer laser lithography generally contains, as a base resin component, a resin having a main chain formed of a structural unit derived from a (meth)acrylric ester; i.e., an acrylic resin, since the resin exhibits excellent transparency at 193 nm or thereabout. As has been known, a photoresist composition containing a polymer containing a structural unit having norbornane lactone exhibits high etching resistance and improved adhesion to a substrate (see Patent Document 1). There has also been proposed, for example, a polymer for a photoresist composition, the polymer containing a structural unit having a norbornane lactone skeleton or norbornane sultone skeleton to which an acryloyloxy group is bonded via a linkage group (see Patent Document 2 or 3).